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January 18, 2009

Loch Lomond has deep canyon underneath

by Sam Savage

The first survey of Loch Lomond in 147 years has found Scotland's most famous loch is 600 feet deep in places with sheer cliffs lining an underwater canyon.

The British Geological Survey used the latest technology -- multi-beam sonar -- to map the floor of Loch Lomond, The Scotsman reported. The last time the bottom of the loch was surveyed, in 1861, Captain H.C. Otter of the Admiralty used fishing line with lead weights attached to take soundings from a rowboat.

Loch Lomond is deeper than the North Sea. The loch was gouged out by a glacier as the last Ice Age ended with a deeply sculpted northern end. The southern end of the loch is wider and shallower.

The challenge was to produce a detailed map of the loch floor, said Alan Stevenson, who led the mapping team. At some points it is 190 meters deep at the north end and you don't find that in the open Atlantic until you get out beyond St. Kilda.

The Loch Lomond and Trossachs National Park plans to make new charts based on the findings and to provide a 3-D image of the loch floor for visitors.

I was amazed by the steepness of the sides of the loch, said Graeme Archibald, the head ranger. It goes down like the Grand Canyon. I have been working on the loch since 1995 but it was only when I saw the BGS maps that I got a real feel for what is underneath the surface.